1. Field of the Invention
The present invention relates to a water-jet propulsion personal watercraft and, more particularly, to an air cleaner box of an engine mounted in a body of the watercraft.
2. Description of the Related Art
In recent years, water-jet propulsion personal watercraft have been widely used in leisure, sport, rescue activities, and the like. The personal watercraft is equipped with an engine mounted within a body surrounded by a hull and a deck covering the hull from above. An air-cleaner box is provided in an internal space of the body and configured to take in air from outside. The air taken into the air cleaner box flows through a throttle body, an air-intake pipe, an air-intake manifold, and the like, and then is delivered to a combustion chamber of the engine.
A water jet pump is provided behind the engine and configured to propel the watercraft. An output shaft of the engine is connected to a pump shaft of the water jet pump through a coupling mechanism provided behind the engine and in the vicinity of an inner bottom portion of the body. Therefore, upon engine operation, the pump shaft rotates integrally with the output shaft. Driven by the engine, the water jet pump pressurizes and accelerates water sucked from a water intake generally provided on a bottom surface of the hull and ejects it rearward from an outlet portion of the water jet pump. As the resulting reaction, the watercraft gains a propulsion force.
In the personal watercraft, water sometimes enters the internal space of the body. And, the water in the internal space of the body may be suctioned into the air cleaner box together with the air within the body.
The water flowing into the air cleaner box together with air might be delivered to the combustion chamber of the engine. In order to avoid this, the air cleaner box is provided at a location above the engine where water is less likely to enter the air cleaner box or forward relative to the engine so as to be distant from the coupling mechanism that would scatter water (see Japanese Laid-Open Patent Application Publication No. 2000-335486).
In the straddle-type personal watercraft equipped with a seat mounted over the deck and straddled by an operator, a deck opening is formed on an upper portion of the deck and below the seat to allow inside and outside of the body to communicate with each other. And, the engine and the air cleaner box are maintained through the deck opening.
In recent years, a four-cycle engine has been put into practical use in place of the conventional two-cycle engine, as the engine mounted in the personal watercraft. The four-cycle engine is constructed such that valve drive system components of the engine such as air-intake and exhaust valves, a camshaft, and the like are provided in the cylinder head located above a cylinder. So, the four-cycle engine has a height larger than that of the two-cycle engine. When the four-cycle engine is mounted in the limited internal space of the body of the watercraft, it is difficult to dispose an air cleaner box above the engine.
The deck opening through which the engine and the air cleaner box are maintained has a limited opening area for keeping rigidity of the body. This leads to limited placement of the air cleaner box. For example, when the air cleaner box is disposed forward relative to the engine, maintenance of the air cleaner box becomes burdensome, because the air cleaner box is relatively distant from the deck opening.